Temperature and relative humidity controller

ABSTRACT

Control systems are provided that provide thermodynamically decoupled control of temperature and relative humidity and/or reduce or prevent frost formation or remove previously-formed frost. The control systems herein may be included as a component of a heating, ventilation, air conditioning, and refrigeration system that includes a heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 16/477,862, filed Jul. 12, 2019, which is a U.S. National PhaseApplication under 35 U.S.C. 371 of PCT/US2018/013228, filed on Jan. 11,2018, which claims the benefit of U.S. Provisional Application No.62/445,434, filed Jan. 12, 2017, which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The invention relates to control systems for thermodynamically decoupledcontrol and maintenance of temperature and relative humidity, forexample, in conjunction with an HVAC system.

BACKGROUND

Current controllers for heating, ventilation, and air conditioning(HVAC) systems are controlled thermostatically and operate based onthermodynamic equilibrium. These thermostats control the temperature asit is coupled to the relative humidity by physical laws. Thesethermostats allow the user to set a desired area temperature, and if thetemperature drops too far below this setpoint, the room will be heated.Alternatively, if the temperature rises too far above this setpoint, theroom will be cooled. Cooling of the air is largely controlled by theremoval of humidity through a condensation process which occurs withinthe HVAC units. In certain interior environments and climates, thethermodynamic coupling of humidity to this thermostatic temperaturecontrol is problematic. For example, when cooling dry air in a desertenvironment, moisture will also be removed, further drying the air andresulting in an uncomfortable living environment. Often in this case,separate pieces of hardware (humidifiers) will be added to solve thisproblem. Some specialty applications, such as server rooms andelectronic assembly areas could greatly benefit from the ability tocontrol the relative humidity as electrostatic discharge is much morecommon in dry environments that occur when indoor air is cooled.

Additional methods for temperature control can be carried out withevaporative coolers. In these systems, moisture is added to low humidityair. The air is cooled adiabatically along a line of constant enthalpy.The resulting air has an increased humidity and reduced dry bulbtemperature.

In addition to the thermostatic (primary) controllers, modern heating,ventilation, air conditioning, and refrigeration (HVAC-R) systems mayinclude sensors for determining inefficient operating conditions such asfrost formation. Furthermore, usage, weather, spatial and temporal datamay be used to manage the operating conditions of HVAC-R systemsincluding operating duty cycles and operation of defrost cycles. Somemodern HVAC-R systems also vary the heat duty of exchangers throughvariable refrigerant flow.

HVAC-R systems coated with hydrophobic materials cause the water to beadon the surface. As the air is pushed across the cooling surface by thefan, the droplets are also dragged across the surface and into acollection pan. Inevitably, some of these droplets will become entrainedinto the air stream and revaporize, resulting in a decrease intemperature of the air stream and an increase in humidity. For typicaluncoated systems, hydrophilic coated systems, and hydrophobic coatedsystems, this droplet revaporization is negligible.

Refrigeration systems need to periodically defrost the evaporator coil,which results in increased energy consumption, equipment downtime,increased equipment cost, and increases in the temperature of theproducts to be cooled. For blast chilling and freezing systems, thisoften requires to the system to stop in the middle of the chilling cycleto defrost the cooling coil. This reduces throughput and results in areduction in quality for the chilled/frozen product.

Improved methods and systems for controlling temperature and humidity,and for chilling materials, are needed.

BRIEF SUMMARY OF THE INVENTION

Control systems and methods of use of the control systems toindependently control (e.g., provide thermodynamically decoupled controlof) temperature and relative humidity, for example, in a room or anenvironment, and/or to reduce or prevent frost formation or to removepreviously-formed frost, e.g., in a device such as a heat exchanger, forexample, as a component of a HVAC or HVAC-R system, are provided.

In one aspect, a control system is provided that providesthermodynamically decoupled control of relative humidity and temperaturein a system such as a heating, ventilation, air conditioning, andrefrigeration (HVAC-R) system, e.g., an HVAC-R system that comprises aheat exchanger. In one embodiment, the HVAC-R system includes a heatexchanger, and the independent (thermodynamically decoupled) controlincludes varying the air velocity through the heat exchanger. In someembodiments, the independent (thermodynamically decoupled) control atleast partially includes jumping droplet condensation on at least onesurface of the HVAC-R system, for example, on at least one surface of aheat exchanger through which the air travels. In some embodiments, thejumping droplet condensation occurs on a nanostructured composition orlayer. In one embodiment, the jumping droplet condensation occurs on ananostructured composition or layer on a structure such as a finstructure, for example, a fin structure that comprises or consists ofaluminum or an aluminum alloy.

In some embodiments, the control system reduces or eliminates frostand/or prevents frost formation. In some embodiments, the independent(thermodynamically decoupled) control includes varying the air velocitythrough the heat exchanger such that the air velocity is greater thanthe critical air velocity for frost formation, thereby preventing theformation of frost. In some embodiments, during at least a portion ofthe time that the control system is in operation, the air velocitythrough the heat exchanger is increased to a value greater than thecritical air velocity for frost formation, thereby removing frost thatformed previously to operation of the control system. For example, insome embodiments, critical air velocity is about 1 to about 20 m/s,e.g., about 3 m/s, for air with relative humidity of 0% to about 100%,about 40% to about 80%, e.g., about 60%, and temperature of about 0° C.to about 60° C., about 5° C. to about 40° C., about 10° C. to about 30°C., or about 15° C. to about 25° C. In some embodiments, the heatexchanger includes a coating composition on at least one surface of theheat exchanger through which air travels, and the onset of frostformation is reduced relative to an uncoated system, thereby preventingformation of frost. In some embodiments, the independent(thermodynamically decoupled) control at least partially includesjumping droplet condensation on at least one surface of the HVAC-Rsystem, for example, on at least one surface of a heat exchanger throughwhich the air travels. In some embodiments, the jumping dropletcondensation occurs on a nanostructured composition or layer.

In another aspect, a controller is provided that decouples (e.g.,independently controls) the control of relative humidity andtemperature. In some embodiments, the controller increases efficiencyand/or reduces energy usage through decreased runtime in comparison to asystem in which relative humidity and temperature are not independentlycontrolled (thermodynamically decoupled). In some embodiments, thecontroller establishes a desired comfort setting for occupants of anenvironment that is exposed to the resultant process fluid, for example,temperature and humidity controlled air. In some embodiments, thecontrol of relative humidity and temperature includes jumping dropletcondensation, for example, on a surface of a heat exchanger, e.g., asurface with a coating layer such as a nanostructured coatingcomposition or layer. In some embodiments, the controller controls afirst setpoint for temperature and a second setpoint for humidity, forexample, in an HVAC-R system.

In another aspect, a coating composition is provided. When deposited onan air-side surface of a heat exchanger, the composition causes a changeon the tube-side temperature, pressure, and/or capacity for heattransfer in the heat exchanger. In some embodiments, the coating isnanostructured. In some embodiments, the coating promotes an increasedcondensate rejection rate in comparison to a surface that does notinclude the coating composition. For example, the increased condensaterejection rate may include jumping droplet condensation or dropletejection.

In another aspect, a heat exchanger is provided that includes a coatingcomposition as described herein on at least one air-side surface.

In another aspect, a controller is provided for a heat exchanger thatincludes an air-side and a tube-side, wherein the controller varies thetube-side temperature, pressure, and/or capacity for heat transfer, forexample, in an HVAC or HVAC-R system. In one embodiment, the controllermodulates cooling capacity of an HVAC or HVAC-R system. In someembodiments, the controller modulates a variable frequency compressor,e.g., an inverter. In some embodiments, control of the tube-sideconditions in the heat exchanger includes a change in the air-side heattransfer rate. In some embodiments, at least one air-side surface of theheat exchanger includes a coating or surface modification, and theair-side heat transfer rate is increased by an increased rate ofcondensate rejection in comparison to a heat exchanger that does notinclude the air-side coating or surface modification. For example, theincreased rate of condensate rejection may include jumping dropletcondensation or droplet ejection. In some embodiments, jumping dropletcondensation or droplet ejection on at least one air-side surface of theheat exchanger may be promoted by a coating or surface modification onthe air-side heat transfer surface. For example, the coating or surfacemodification may include a nanostructured composition. In an embodiment,the heat exchanger surface that includes a coating or surfacemodification, e.g., a nanostructured coating composition or layer,comprises or consists of aluminum or an aluminum alloy.

In another aspect, a controller is provided that controls air velocityand coolant temperature, pressure, and/or capacity to achieve a desireddecoupled (e.g., independently controlled) air temperature and airhumidity output condition in an HVAC or HVAC-R system.

In another aspect, methods and systems are provided to achievefrost-free blast chilling and or reduced-frost blast freezing by usingdroplet ejection surface modified evaporator coils and thermal controlof the coil temperature as part of the refrigeration system. Dropletejection coatings are able to suppress frost formation below thefreezing point of water. This provides completely or substantially frostfree blast chillers and blast freezers with fewer defrosts when operatedin a prescribed manner. Droplet ejection surface modifications reducethe rate of frost formation or prevent the formation of frost altogether(FIG. 7 ).

The refrigeration system can be operated under several possible modes,(a) cooling; (b) freezing; or consecutive modes (a)+(b). Under coolingmode (a), the refrigeration system will operate at a temperaturesufficient to rapidly chill products and remain above the temperaturefor onset of frost formation on the evaporator coil. Due to the dropletejection surface modification, the coil can maintain temperatures below0° C., about 0° C. to about −25° C., about −5° C. to about −10° C., orany of about −5° C., about −10° C., about −15° C., about −20° C., orabout −25° C., without frost formation on the coil. In some embodiments,the operation of the system occurs within the temperature and airvelocity range depicted in FIG. 7 . Operation in this range allows forthe rapid chilling of products without frost formation on the coil andthe commensurate defrosting related problems.

When operating in freezing mode (b), the refrigeration system lowers thecoil temperature to rapidly freeze the products until the desired setpoint is achieved. By initially operating in refrigeration mode (a)outlined above and transitioning into freezing mode (b), the air will bedehumidified and the vapor pressure of water will be reduced. Whenoperating in these consecutive cooling and freezing modes (a)+(b), thefrost formation is minimized via the previous dehumidification in thechilling mode, with condensate drainage instead of frost formation. Theresult of operation in these consecutive modes is an increasedthroughput of chilled product for a given refrigeration system. Forexample, throughput may be increased at least about 10% or at leastabout 20%.

These two techniques reduce frost formation which improves coil andsystem performance and improves the throughput of chilled productsthrough a refrigeration system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts controller versus conventional cooling paths in an HVAC-Rsystem in a hot and dry environment.

FIG. 2 depicts controller and convention cooling path in an HVAC-Rsystem under hot and humid outdoor conditions.

FIG. 3 depicts interaction of a controller as described herein within anHVAC-R system.

FIG. 4 shows a 9 mm wide field image. The nanostructured surface islocated on the bottom portion of the figure. Liquid droplets of varyingsize can be seen. The white area to the top is the background, uncoatedsubstrate which readily shows frost formation. The operating velocityfor this image is above the critical velocity for frost formation.

FIG. 5 shows operating regimes for air velocity that can be used as partof a control algorithm to avoid or minimize frost formation.

FIG. 6 shows a sample under conditions leading to frost formation(t=0-12 minutes) and defrosting (12-13.5 min). Velocity profiles forthese test configurations are shown in the top portion of the figure.

FIG. 7 shows the observations of the onset of frost on droplet ejectioncoated coils and uncoated coils for saturated air as a function of inletair velocity and temperature. In this figure the inlet air is saturated,but similar plots may be generated as a function of inlet relativehumidity.

DETAILED DESCRIPTION

Control systems and controllers are provided that independently regulatetemperature and relative humidity, for example, in an HVAC or HVAC-Rsystem. Temperature and relative humidity are thermodynamicallydecoupled in the systems described herein.

Superhydrophobic materials are known that allow droplets to eject or“jump” from the surface at a very small size, which can increase thequantity of entrained droplets by many orders of magnitude in comparisonto unmodified, hydrophilic or hydrophobic surfaces. Entrained liquidfrom these latter surfaces comes about from large turbulence or sheddingactions. The resultant droplets are large and revaporization rates arelimited. In contrast, on certain superhydrophobic surfaces, very largenumbers (e.g., millions) of droplets per second are entrained andcarried downstream. Additionally, these droplets are small enough toquickly revaporize and transfer the latent heat to cool the air whilesimultaneously increasing the humidity. Such materials are describedherein in relation to heat exchange and consequent control oftemperature and relative humidity (RH).

The quantity of droplets jumping or ejecting from the surface to becomeentrained is a function of the air velocity in a heat exchanger. Bycontrolling the face velocity across the exchanger, the amount ofrevaporization can be controlled, thus allowing for a range ofindependent temperature and RH options, instead of the coupledtemperature and RH control offered by current thermostatic systems.Additionally, controlling the degree of condensation driving forcethrough the difference in temperature between the refrigerant (tubeside) and air side (fin side) in a heat exchanger will affect the degreeof droplet ejection and revaporization. This may be achieved in avariety of ways, including but not limited to, refrigerant flow rate,refrigerant temperature via control of compressor (refrigerantpressure), and/or airflow as noted above.

In some embodiments, the change in face velocity and latent degradationphenomenon described herein is promoted by a coating composition thatcauses a shift in the tube-side equilibrium in the heat exchanger. Insome embodiments, the coating composition includes a nanostructuredmaterial. In some embodiments, the nanostructured material promotesdroplet ejection from the surface. A significant increase in theair-side heat transfer coefficient can greatly increase the capacity ofa heat exchanger, and consequently, an increase in capacity of thetube-side will also be required. This can be accomplished by a variablecapacity compressor such as an inverter compressor.

This new coupling of air velocity, air cooling capacity, andconsequential tube-side capacity requires novel control systems tomaximize the functionality of the coated HVAC-R system and to maximizeits efficiency of operation. A schematic of an example control system isshown in FIG. 3 .

In certain embodiments, the conditions of the incoming air and fintemperature lead to the formation of frost from the condensate on theexchanger. This frost formation limits the heat transfer from theevaporator, reducing the amount of useful cooling from the device, andfurther, increases the pressure drop across the evaporator coils, whichadversely affects energy efficiency.

In certain embodiments, with a nanostructured coating applied asdescribed herein, we have surprisingly shown that at certain velocitiesin which frost formation readily occurred on materials withoutnanostructured coatings (i.e., velocities obtainable in a typical HVACsystem), frost formation was not observed. An example of this phenomenonis shown in FIG. 4 . Condensation was observed to continue in theunfrozen regions.

In certain embodiments, an HVAC-R system design is provided in which thedesign air velocity is greater than the critical air velocity for aparticular nanostructured surface, in which the onset of frost formationis severely retarded or even prevented altogether. In certainembodiments, it is desirable that the velocity across the surface shallbe minimized to limit pressure drop and potential noise generation.

Surprisingly, we have also observed that changing air velocity alone wassufficient to defrost samples that had a nanostructured coating applied.In this scenario, a sample was subjected to conditions which led tofrost formation. At this point, the air velocity was increased, and thefrost which had formed under the previous conditions was removed toliquid water, and removed from the sample.

In some embodiments, a HVAC-R control system design is provided in whichthe primary operating air velocity may lead to conditions in which frostformation may occur in a prescribed or otherwise controlled manner, andthe primary air velocity is increased to remove any potential frostformation and to prevent the additional formation of frost and thecommensurately deleterious outcomes. The periods of increased velocitymay be relatively frequent to prevent frost formation and to preventheat transfer fouling by frost, or may be relatively infrequent toremove frost which has formed.

Air velocity may be modulated by fan speed, pitch, or proximity, bypassventing, baffling or dampers (the latter being the case for an inletcooler for a turbine in which the turbine is downstream and is the primemover of the process fluid (air), and velocity may be changed byaffecting damper position on the front end).

Definitions

“A,” “an” and “the” include plural references unless the context clearlydictates otherwise.

A “nanostructured” coating refers to a coating composition that has afeature in at least one dimension that is less than 100 nanometers.

“Non-condensing gases” or “NCGs” refers to gasses that do not changephase at the desired condensing conditions of a vapor. Oxygen andnitrogen, for example, are NCGs when air is being dehumidified.

“Condensing conditions” refers to a condition wherein a surface iscooled below the dewpoint of a vapor.

“Supersaturation” refers to a condition when the vapor pressure of avapor is above the equilibrium vapor pressure at a given temperature andpressure. A supersaturation of 1 refers to a relative humidity of 100%and any further increase promotes condensation.

“Ejection,” in reference to droplets of liquid, refers to leaving asurface with a velocity that has a non-zero normal component.

“Surface tension” refers to the tension of a liquid surface caused bycohesive forces in the bulk of the liquid that pulls inward toward thebulk and tends to minimize the surface area for a given volume.

“Droplet adhesion forces” refers to the forces responsible for causing adroplet to pull outward and spread on a surface, thus preventing it fromforming a sphere. Contrarily, “cohesive forces” are those forces thatcause a droplet to pull itself inward and form a sphere, such as surfacetension.

“Refrigerant” refers to a substance or mixture used in a refrigerationcycle as the working fluid. This fluid often goes through phase changes,but need not to be effective. Commercial refrigerants include, but arenot limited to R-22, R-134a, R-401 and other formulations. A nonlimitinglist of refrigerants can be found athttps://en.wikipedia.org/wiki/List_of_refrigerants.

“Working fluid” refers to a liquid or gas that absorbs or transmitsenergy. For example, the working fluid in an air conditioner system isthe coolant such as Freon, glycol, ammonia, propane, or water that isused to cool the process fluid.

“Process fluid” refers to a liquid or gas that is treated by interactionwith the working fluid. For example, in an air conditioner system, theprocess fluid is the air that is cooled.

“Sensible heat” refers to a change in temperature of a gas or objectwith no change in phase.

“Sensible heat ratio” refers to the ratio of the sensible coolingcapacity to the total cooling capacity.

“Control system” or “controller,” used interchangeably herein, refers toa device controlling logic, machine code, designs, concepts,configuration and/or supporting hardware.

“Relative humidity” refers to the amount of water vapor present in airexpressed as a percentage of the amount needed for saturation at thesame temperature.

“Air-side” in reference to a heat exchanger refers to the surfacesadjacent to and regions concomitant with the process fluid, for example,air to be cooled.

“Air side heat transfer rate” refers to the amount of heat transferredfrom the process fluid to the primary evaporator device.

“Tube-side” in reference to a heat exchanger refers to the surfacesadjacent to the working fluid, for example, refrigerant.

“Condensate rejection rate” refers to the amount of condensate condensedfrom the air stream and removed from the primary heat transfer surfacesper unit time.

“Jumping droplet condensation” or “droplet ejection” refers tocondensate formed on the primary heat transfer surfaces wherein thedroplet leaves the surface with some velocity out of plane of theprimary heat transfer surface (as opposed to rolling along the surface,finding an edge and separating). Often, but not necessarily, thedroplets are being subjected to an external force (drag, vibration,coalescence, gravity, etc.).

“Throughput” refers to the amount of a product or commodity that may bechilled or frozen per unit time (e.g., pounds per day).

Controller

A diagram indicating a non-limiting example of how a controller asdescribed herein may interface within an HVAC-R system is shown in FIG.3 . In this case the controller is operating as a negative feedbackcontroller wherein the input temperature and humidity setpoints aresubtracted from the sensor readings of the air output. This differentialerror of the setpoint is reduced by the controller modulating the airspeed to increase or decrease the effect of droplet ejection, and thuslatent degradation. For example, in some embodiments, the controller mayoperate the air speed at about 300 feet per minute (fpm) for a portion,e.g., a majority, of the time, and increase the velocity to about 600fpm to about 800 fpm or about 1000 fpm to remove frost formation, thenreturn to about 300 fpm. The air speed can be modulated by changing thefan speed. Additionally, the compressor capacity is controlled bychanging the frequency of a variable frequency drive. The benefits ofthis control system with droplet ejection coatings on the coils isdecoupled output air temperature and humidity and more efficientoperation.

Systems described herein (e.g., nanostructured coated heat exchangers)may be used within existing controller systems, such as a variablerefrigerant flow system, to control the tube side HVAC conditions. Insome embodiments, variable refrigerant control can be achieved viavariable refrigerant compressor speed or variable pressure drop throughexpansion valve control.

Refrigeration systems herein may be controlled to operate within a frostfree region to prevent the requirement for defrost. This operating rangemay be determined through the generation of an inlet humidity,temperature and velocity plot such as that shown in FIG. 7 . Systems maybe monitored for refrigerant pressure temperature and mass flow. Systemsmay be monitored for inlet air humidity, temperature and velocity.Systems may be monitored for combinations of parameters therein. Airvelocity and refrigerant mass flow may be controlled through valvesand/or programmable fan motors or other means known to those skilled inthe art. As an example, an algorithm may be developed and employed tocontrol the speed of a fan wherein the result is avoidance or modulationof frost formation. Examples of operating regimes and control algorithmsfor the control of frost are provided in FIGS. 5 and 6 .

Droplet Ejecting Coatings

In some embodiments of the temperature and relative humidity controlsystems described herein, droplet ejecting coating materials areprovided that eject condensed droplets of liquid from the surface of asubstrate, e.g., a surface of a heat exchanger, e.g., in an HVAC system.In some embodiments, a droplet ejecting coating material includes ananostructured material deposited on a substrate, and optionally, ahydrophobic material deposited on the nanostructured material. Thenanostructured material includes a geometry that provides a drivingforce for droplet ejection from the surface. The geometry may include,but is not limited to, a nanostructure that causes the droplets to takea distorted shape upon condensation.

Droplet ejecting coating materials may include a surface that istextured such that condensed droplets are ejected when the surfacetension force exceeds the droplet adhesion forces, thereby resulting ina net force vector that has a component out of the plane of thesubstrate.

The coating materials disclosed herein may eject condensed fluid fromthe surface in the presence of one or more non-condensing gases (NCGs).For example, the coating materials may eject fluid in the presence ofair, gas components of air, or inert gases. In some embodiments, the NCGis selected from air, nitrogen, oxygen, carbon dioxide, hydrogen,helium, argon, or a combination thereof. In some embodiments, the NCG isselected from air, oxygen, nitrogen, carbon dioxide, argon, or acombination thereof. In one embodiment, the NCG is air.

The coating materials disclosed herein may eject condensed fluid fromthe surface at supersaturation greater than about 1.0, about 1.1, about1.2, or about 1.25, or at supersaturation about 1.0 to about 1.1, about1.1 to about 1.25, about 1.1 to about 3.0, or about 1.1 to 5.0.

Condensed fluid droplets that may be ejected by the coating materialsdisclosed herein include, but are not limited to, water, ethanol, andrefrigerants. In some embodiments, the condensed fluid is selected fromwater, ethanol, a hydrofluorocarbon (HFC), and a hydrofluoro-olefin(HFO), or a combination thereof. In some embodiments, the condensedfluid is selected from water, ethanol, difluoromethane (HFC-32),difluoroethane (HFc-152a), pentafluoroethane (HFC-125),2,3,3,3-tetrafluoropropene (HCO-1234yf), 1,3,3,3-tetrafluoropropene(HFO1234ze), or a combination thereof. In one embodiment, the condensedfluid is water. In some embodiments, the condensed fluid is anindustrial process or working fluid.

Droplet ejecting coating materials as described herein may ejectcondensed fluid droplets from the surface having an average diameter ofless than about 2 millimeters, less than about 1 millimeter, or lessthan about 500 micrometers.

In some embodiments, the nanostructured coating layer includesnanostructured metal, ceramic, glass, or polymer.

In some embodiments, the nanostructured coating layer includes a ceramicthat is a metal oxide. The metal oxide may be, for example, a transitionmetal oxide, tin(IV) oxide, magnesium oxide or aluminum oxide. In someembodiments, the transition metal oxide is selected from zinc oxide,iron(II, III) oxide(Fe₃O4), iron(III) oxide (Fe₂O₃), manganese(IV) oxide(MnO₂), manganese(II, III) oxide (Mn₃O₄), manganese(III) oxide (Mn₂O₃),nickel(II) oxide (NiO), nickel(III) oxide (Ni₂O₃), zirconium(IV) oxide(ZrO₂), titanium(IV) oxide (TiO2), chromium(III) oxide (Cr₂O₃),copper(II) oxide (CuO), cobalt(II) oxide (CoO), cobalt(III) oxide(Co₂O₃), and cobalt(II, III) oxide (Co₃O₄).

In some embodiments, the nanostructured coating layer includes a glass.In some examples, the glass includes silica or a silicate.

In some embodiments, the nanostructured coating layer includes apolymer. In some examples, the polymer is a fluoropolymer, polyethylene,or polypropylene. In some embodiments, the polymer is a fluoropolymerselected from polytetrafluoroethylene (PTFE), polyvinylidene (PVDF),polyvinylfluoride (PVF), and fluorinated ethylene propylene (FEP), or acombination thereof. In some embodiments, the polymer is a blockcopolymer, for example, but not limited to, wherein each block of thecopolymer is less than about 500 monomer units, or less than about 200monomer units. For example, the block copolymer may be a hydrophobicpolymer that includes two or more monomer units. In some embodiments,the block co-polymer may include one or more monomers, such as, but notlimited to, propylene, ethylene, tetrafluoroethylene, trifluoroethylene,vinylfluoride, hexafluoropropoylene, 1,1-difluoroethylene,1,2-difluoroethylene, and isobutylene.

In some embodiments, a hydrophobic coating layer may include one or morehydrophobic functionality selected from alkyl, vinyl, phenyl, andfluoroalkyl. For example, the hydrophobic functionality may include, butis not limited to, alkylsilane, vinylsilane, phenylsilane, orfluoroalkylsilane. In certain nonlimiting embodiments, the hydrophobicfunctionality is hexamethyldisilazine, sodium methylsiliconate,potassium methylsiliconate, dimethiconol, perfluorooctyltriethoxysilane,perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane,perfluorodecyltrimethoxysilane, octadecyltriethoxysilane,methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane,isobutyltriethoxysilane, or phenyltriethoxysilane. In some embodiments,the hydrophobic coating refers to a coating that when added to a smoothsubstrate, imparts a contact angle greater than or equal to 90 degrees.

Methods of Making Droplet Ejection Coatings

Methods of making coatings that eject droplets of condensed liquid froma substrate, e.g., under condensing conditions, are provided. In certainnon-limiting embodiments, the methods include: (a) depositing ananostructured coating layer on a substrate; and optionally (b)depositing a hydrophobic functional layer, i.e., a hydrophobic materialthat includes one or more hydrophobic functional groups, on the surfaceof the nanostructured material.

The nanostructured layer may be deposited on the substrate by anysuitable means, including but not limited to, sol get processing,chemical bath deposition, dip coating, spray coating, physical vapordeposition, or chemical vapor deposition. In one embodiment, thenanostructured coating is a metal oxide that is deposited by, forexample, sol gel processing, chemical bath deposition, or dip coating.The hydrophobic functional layer may be deposited onto thenanostructured layer by any suitable means, including but not limitedto, vapor deposition or dip coating.

Nonlimiting examples of nanostructured and hydrophobic coating materialsare described above. The substrate may include a metal, metal alloy,glass, or ceramic material.

In some embodiments, the substrate is pretreated prior to deposition ofa coating composition, e.g., a nanostructure coating layer as describedherein, to remove debris or substance(s) on the surface and/or to smooththe surface (i.e., to access the substrate to promote adhesion and toprevent defects), with one or more treatment(s) selected from cleaning,degreasing, rinsing, etching, desmutting, oxidizing, removing previoustreatments, roughening, planarizing, steam cleaning, thermal oxidation,and smoothing.

The following examples are intended to illustrate, but not limit, theinvention.

EXAMPLES Example 1

In a hot and dry environment, 37° C., 20% relative humidity (RH) forexample, a controller as described herein operates in a conventionalcooling mode at face velocities such as 0 to about 3 m/s, for example,about 1.5 m/s and cools the air sensibly to the desired comfortablerange. Alternatively, if the operator desires a higher relative humidityand lower power consumption or the controller is programmed to minimizeenergy consumption, the face velocity is increased to about 1 to about20 m/s, for example, about 3.0 m/s which will cause a greater dropletejection rate, increasing the revaporization rate. This increases thehumidity and decreases the temperature. The controller enables the HVACsystem to operate as a conventional forced air coil and evaporativecooler, simultaneously.

FIG. 1 shows the cooling paths on a psychrometric chart. A controllerenabled cooling path (1→2→4) is shown versus the conventional cooling(1→2→3) path, when the operator desires higher humidity. The coolingunit operates conventionally and the controller turns on at point 2 andincreases the fan speed to raise the humidity, providing additionalcooling capacity due to latent degradation, and increasing the overallefficiency of the unit to achieve conditions in the comfort region. Thiscontrolled latent degradation route allows simultaneous evaporativecooling and forced air cooling, reducing the energy usage by more than50%.

Example 2

A controller as described herein advantageously operates in hot andhumid environments, for example, under outdoor conditions of 30° C. and80% RH. The high humidity environment cannot use any additional latentdegradation. The controller therefore allows the unit to cool using theconventional operating route to minimize energy usage for the desiredsetpoint. This cooling path is plotted in FIG. 2 .

In a hot and humid environment, the controller does not increase the fanspeed and follows the conventional cooling path. In this case, this isthe most energetically efficient route to cool due to the low sensibleheat ratio. The controller is programmed to acknowledge this to operatethe unit as efficiently as possible.

Example 3

An aluminum plate, with a nanostructured coating applied as describedherein, approximately 30 mm by 40 mm, was placed into a wind tunnel andmounted to a cold plate with estimated temperature of −15° C. Uncoatedaluminum located adjacent to the plate was covered with frost. Airflowconditions were ˜20° C., 60% RH. The flow velocity across the plate wasapproximately 5 m/s. These conditions were maintained for over 1 hr.Frost was observed on uncoated sections, whereas the nanostructurecoated materials only showed condensation. After steady state conditionswere observed, the flow velocity was reduced to 2 m/s. After a fewminutes, freezing of droplets and frost formation were observed on boththe nanostructure coated sample and the uncoated materials. After aperiod of 12 minutes, the velocity was returned to 5 m/s and on thefrosted surface, melting of ice and frost was noted. In approximately 90seconds, the previously observed steady state conditions werereestablished. Results are shown in FIG. 6 .

Example 4

A fin and tube heat exchanger, with surface modified fins that contain asurface material that promotes droplet ejection, was placed in acontrolled cooling environment wherein the inlet air conditionsincluding humidity and temperature were controlled.

This system used a recirculating chiller on the tube side filled with aglycol-water mixture. This water side loop was measured for inlettemperature, outlet temperature, and coolant flow. These measurementsallowed for the calculation of the heat transferred into therefrigerant.

The air flowing across the heat exchanger was also measured for inlettemperature, outlet temperature, inlet relative humidity, outletrelative humidity, and volumetric flow. These measurements were used tocalculate the amount of energy removed from the air as it crossed theheat exchanger.

One coil with droplet ejection coating was tested. Another coil with nodroplet ejection was tested in a similar manner. The coils weresubjected to inlet air velocities of 200 to 500 feet per minute. Inletair was saturated with water (RH 100%) and inlet air temperature wasvaried from 0 to 6° C. below freezing. In these tests, the coolant flowwas set to ensure minimum differences between the inlet air and coolanttemperature. The coils were visually observed for the onset of frostformation.

The surfaces with droplet ejection coating required lower inlettemperatures to observe frost formation than those surfaces withoutdroplet ejection coating. The degree of frost onset depression is afunction of air velocity, ranging from about −4° C. below at lowvelocity to about −6° C. at high velocities. The velocity rangescorrespond to typical HVAC conditions, but the mechanism shall apply toa wider range of velocities. An uncoated coil showed the onset of frostat about −1.5° C. at low velocity to about −3° C. at high velocity.These results are shown graphically as FIG. 7 .

Example 5

Large blast chillers bring in a large amounts of produce tochill/freeze. Current systems are capable of freezing product at a rateof 10,000 pounds (lbs) of product per day. This limit may be set by theamount of time required to defrost the cooling coils. As an example, thecooling coils may operate for 11 hours and require a 1 hour defrostcycle. Operation with droplet ejection coatings and embodiments ofoperating conditions described herein provide continuous operationwithout the need for defrosting. This results in the ability to processabout 11,000 lbs/day of product—a 10% increase in facility throughput.

Although the foregoing invention has been described in some detail byway of illustration and examples for purposes of clarity ofunderstanding, it will be apparent to those skilled in the art thatcertain changes and modifications may be practiced without departingfrom the spirit and scope of the invention. Therefore, the descriptionshould not be construed as limiting the scope of the invention, which isdelineated in the appended claims.

All publications, patents, and patent applications cited herein arehereby incorporated by reference in their entireties for all purposesand to the same extent as if each individual publication, patent, orpatent application were specifically and individually indicated to be soincorporated by reference.

We claim:
 1. A coating composition comprising a structured surface thatconsists of nanostructured features, wherein the coating compositionwhen deposited on an air-side surface of a heat exchanger that comprisesan air-side and a tube-side causes a change in temperature, pressure,and/or capacity for heat transfer on the tube-side of the heat exchangerwhen the heat exchanger is in operation.
 2. The coating compositionaccording to claim 1, wherein the coating composition comprises anincreased condensate rejection rate on a surface on which it isdeposited in comparison to a surface that does not comprise the coatingcomposition.
 3. The coating composition according to claim 2, whereinthe increased condensate rejection rate comprises jumping dropletcondensation or droplet ejection.
 4. A heat exchanger that comprises anair-side and a tube-side, wherein an air-side surface of the heatexchanger comprises a coating composition comprising a structuredsurface that consists of nanostructured features.
 5. The heat exchangeraccording to claim 4, further comprising delay or prevention of frostformation when the heat exchanger is operated below the freezing pointof water in comparison to a heat exchanger that does not comprise thecoating composition, wherein the delay or prevention of frost formationcomprises liquid condensate rejection from the structured surface of thecoating composition by droplet ejection.